Cooking device with blower and water inlet

ABSTRACT

A cooking device comprises a cooking chamber ( 11 ) and one or more heating elements ( 12 ). Furthermore, a blower ( 20 ) is provided, which comprises a radial blower impeller ( 22 ) and an atomisation element rotating with the radial blower impeller ( 22 ). A water supply ( 30 ) comprises at least one water outlet ( 33 ), which supplies water onto the atomisation element ( 25 ). An evaporation of the water and thus a humid cooking chamber air is achieved. The atomising element is a discoidal, axially-symmetrical element, the outer radius of which is the same as, or larger than the inner radius of the blade region of the radial blower impeller ( 22 ). The atomisation element is arranged adjacent to the radial blower impeller in the axial direction and the water outlet ( 33 ) is arranged adjacent to the atomisation element ( 25 ), outside the radial blower impeller ( 22 ).

The invention relates to a cooking device comprising a cooking area, oneor more heating elements, a fan incorporating a radial flow impellerhaving a blade region, a disk-shaped axially-symmetrical atomisationelement which rotates with the radial flow impeller, and a water supplyhaving at least one water outlet which delivers water to the atomisationelement.

Cooking devices are being equipped to an increasing extent with a steamgenerating system for improving the results of the cooking process withthe help of the damp air which then ensues in the cooking area. Suchcooking devices are, for example, combination steamers, baking-ovens orhot-air ovens. They serve, in particular, for the purposes of preparingfood for consumption. On the one hand hereby, it is possible to producesteam by means of a steam generator located externally of the cookingarea and then feed this steam into the cooking area through a connectingmember.

However, in another concept of increasing interest, the steam is not fedinto the cooking area from an external source but is produced directlyin the cooking area. To this end, water is supplied to the cooking areaand distributed therein in different forms and is thus evaporated by thehot environment.

For this purpose, water supply pipes are employed in accordance with theconcepts known from EP 0 233 535 B1, EP 0 383 366 B1 or EP 0 640 310 B1for example, said pipes supplying the water to the hub of the fan in acentrifugal fan. Due to the fact that the hub is rotating, the water isfed from the hub to the impeller blades of the fan by centrifugal forceand there, the water is decomposed insofar as possible into drops whichshould then evaporate in the hot atmosphere of the cooking area. Hereby,the hub is approximately cylindrical in the case of EP 0 233 535 B1 andEP 0 383 366 B1, whilst EP 0 640 310 B1 proposes a pre-atomising memberwhich is approximately spherical in shape and thus possesses a convexsurface and hence is better at distributing the droplets.

In each of the respective proposals in accordance with DE 197 31 544 A1and DE 41 31 748 C2, there are provided pre-atomising members in theform of disks which are located within the radial flow impeller androtate with the hub. The disks are axially symmetrical. The water isdelivered externally to the outer periphery of the disk in a radialdirection in the case of DE 197 31 544 A1, whereas it impinges a verysmall part of the disk at an angle in DE 41 31 748 C2.

Herein, the heating of the atmosphere in the cooking area is effected byelectrical heating elements or else by means of heat exchanger pipesthrough which there flows a hot medium so that they too function as aheating element. These heating elements are usually disposed directly inthe flow path of the impeller in order to distribute the ensuing heat ina uniform manner.

Similar concepts are proposed in both EP 0 244 538 B1 and EP 0 523 489B1, whereby here, the water is supplied internally in axially parallelmanner to the interior of the hub from outside the cooking area throughcentral passages in the hub, from where it is likewise distributedoutwardly onto the fan blades. So as to make this possible, complicatedseals and co-rotating clamping devices must be provided in order tomaintain the stability of the cup-like hub (EP 0 244 538 81) or thecone-like extended hub (EP 0 523 489 B1), to prevent water seepage atunintentional places and in order to ensure proper functioning.

The disadvantage with all of the aforementioned concepts is that theperipheral speed of the described hub components is naturally relativelyvery low due to the proportionately small diameter of the hub. Thisrelatively low peripheral speed leads to a relatively small centrifugalforce and thus to a non optimal distribution of the water droplets whichremain relatively large. If one were to increase the rotational speed ofthe fan i.e. the rotational speed of the fan motor in the fan in orderto improve the effectiveness of the arrangement, then this would lead tothe need for higher powered motors thereby increasing the costs both forthe cooking device and for the operation thereof, this being somethingthat is not desired. In addition, the higher air speeds then ensuing inthe cooking area are neither necessary nor desirable.

Constructions have therefore been proposed in EP 0 457 971 B1, DE 40 13596 C2 and DE 41 25 696 C1 wherein the water is not conveyed to the hub,but rather, is introduced into the air inlet region of the fan anddistributed from there. Thereby, the water runs over a complicatedcascaded distribution structure in EP 0 457 971 B1, it impinges directlyon the blades in DE 40 13 596 C2, and, in DE 41 25 696 C1, it isproposed that the water be distributed individually via a plurality ofwater supply devices and delivered in front of the respective heatingelements. The disadvantage of these constructions is the relatively highexpenditure and the complexity of the final installation. This leads tohigh costs and, in particular, makes cleaning of the correspondingcooking devices substantially more difficult. In addition, theuniformity of the distribution process and thus the efficiency of thearrangements are unsatisfactory.

In contrast thereto, the object of the invention is to propose a cookingdevice in accordance with the preamble of the main Claim wherein, withthe aid of a device that is as constructionally simple as possible,there will nevertheless be obtained droplets of as small a size aspossible which can then rapidly evaporate in the hot ambient air andthus achieve a high level of efficiency.

This object is achieved in that the atomisation element has an externalradius which is the same as or greater than that of the inner radius ofthe blade region of the radial flow impeller, in that the atomisationelement is arranged adjacent to the blade region of the radial flowimpeller in the axial direction, and in that the water outlet isarranged in the neighbourhood of the atomisation element on the sidethereof remote from the blade region of the radial flow impeller.

The object is achieved in a surprising manner by virtue of thissolution. The water from the water outlet now impinges on an atomisationelement which, in contrast to EP 0 640 310 B1 or the earlier state ofthe art, is of large radius so that the spin-off speed will be verysubstantial due to the centrifugal force at the periphery of thisatomisation element. At the same time, the quantities of water filmdistributed on the individual peripheral portions are also very muchsmaller and the film is very much thinner due to the largecircumference, this thereby substantially favouring the formation ofsmall droplets. The small droplets can then evaporate without difficultyin the atmosphere of the cooking area.

It is preferred that the atomisation element should be on that side ofthe radial flow impeller which is remote from the neighbouring wall ofthe cooking area. The air flow and the arrangement of the heatingelements then lead to a better evaporation effect.

It is of very especial advantage, if the atomisation element is also thecover plate of the radial flow impeller at the same time. In any case,for the purposes of stabilizing the blades thereof, radial flowimpellers already have a cover plate for holding these blades togetheron the side remote from the cooking area wall. This cover plate is aperforated plate which comprises a uniform, circularly symmetricalcentral hole in the region near the axis for the purposes of providingan entrance for the atmosphere of the cooking area which enters theradial flow impeller at this point in order to be spun outwardly in theusual manner. It does not have to be held on the axis since it is ofcourse already connected to the blades in the blade region.

In the preferred embodiment of the invention, this cover plate can nowtake on the auxiliary task of catching the water originating from thewater outlet and conveying it outwardly by centrifugal action.

Thus, other than is the case in practically all of the conceptions inthe state of the art, the water no longer reaches the impeller blades.Conventionally, it had always been assumed that it was precisely theseblades that were necessary in order to finely distribute the waterdroplets just by means of the force with which the water droplets struckthere and burst apart. This latter effect does in fact occur, but thesymmetrical, although not continuously running blade surfaces also leadto an intermittent distribution of the water droplets which, moreover,are braked in their flight and thus condense again instead of continuingthe evaporation process that began when they were spun-off.

Now, in addition to the previously mentioned positive effect of spin-offfrom a position located substantially more distantly from the axis, theinvention completely avoids the impingement of the water droplets on theblades of the impeller.

On the one hand, the water is now guided into a region where it ispossible for the spin-off action produced by the centrifugal force to beeffected at a very high speed, this thereby favouring the formation ofvery small droplets and thus increasing the evaporation effect and theefficiency.

On the other hand, it is at the same time possible to form a very thinwater film since the distributed quantity of water is distributed over alarge surface area and, due to the outward flow, it is also distributedover a very large periphery in proportion to the hub. The quantity ofwater per unit of periphery, i.e. per length, is very much smaller thanin the case where spin-off occurs from the hub, this likewise favouringthe formation of very small droplets with the same advantageousconsequences.

At the same time, one can dispense with the provision of complicatedconstructions, possibly with re-entrant angles and regions that aredifficult to clean. The only thing needed is a means for the supply ofwater to a readily accessible and thus easily cleanable position in thecooking area, namely, in front of the radial flow fan as seen by theuser. Moreover, use is made of the exterior of the cover plate which ofcourse already exists in the known radial fans and now merely serves anauxiliary purpose. In addition, this exterior of the cover plate is veryeasy to clean. If chalk deposits should develop, they can easily beremoved from the surfaces since these are readily accessible, have nore-entrant angles and are also relatively flat. Moreover, thedevelopment thereof is also reduced due to the high speeds.

Thus, there are neither extensive auxiliary installations which createcosts and make cleaning more difficult, nor is there a risk ofcalcification and blockage of the supply holes. Instead, the smallest ofwater particles are spun-off and the evaporation process is enhanced dueto the advantageous use of a relatively large spin-off radius.

It is particularly preferred that the cover plate be provided with aradially symmetrical surface structure which forms a circumferentialchannel.

These effects are thereby reinforced, and the water emerging from thewater outlet in the proximity of the cover plate can be collected in aparticularly simple and at the same time secure manner, and uniformdistribution of the water over the entire surface of the cover plate isensured.

Moreover, it is particularly preferred that the cover plate of theradial flow impeller should be arranged radially symmetrically at anangle relative to the base plate which is greater than 5° and less than90°.

In this way, premature separation of the water from the cover plate isreliably prevented and maximum acceleration of the water when beingspun-off the outer periphery of the cover plate is achieved due to theadditionally developed contact pressure.

An exemplary embodiment of the invention is described in more detailhereinafter with the aid of the accompanying drawing.

Therein:

FIG. 1 shows a sectional, schematic view of a cooking device accordingto the invention; and

FIG. 2 an enlarged illustration of the cover plate of the radial flowimpeller in the embodiment depicted in FIG. 1.

A cooking device, for example a combination steamer, a baking-oven orother type of hot-air device is schematically illustrated in FIG. 1 inthe form of a sectional view as seen by the user. This cooking device 10includes a cooking area 11. A heating element 12 is provided in thecooking area 11 at the left-hand side although only twoschematically-indicated turns thereof can be perceived. The heating ofthe cooking area 11 can be effected either by means of electricalheating elements 12 or else by means of heating elements 12 in the formof heat exchanger pipes through which a hot medium flows. Other types ofdevice for producing heat could also be employed as heating elements 12.

A fan 20 is provided in order to uniformly distribute the heat producedby the heating element 12 or the air that has been heated therebythroughout the cooking area 11. This fan 20 includes a fan motor 21which drives a radial flow impeller 22 in the cooking area 11. Theradial flow impeller 22 is located within the heating element 12 and isradially surrounded thereby. The heating elements 12—whether electricalor in the form of heat exchanger pipes—are generally mounted in thedirect field of flow from the radial flow impeller 22. Otherarrangements are possible, but this has proved to be effective. Theradial flow impeller 22 comprises a base plate 23 upon which there arearranged a plurality of blades 24 that are perpendicular relative to thebase plate 23 and radial relative to the axis. Thus, in like manner tothe axis of the heating element 12, the axis of the radial flow impeller22 lies in the plane of the picture in FIG. 1 and it extendshorizontally therein. It follows therefrom that the base plate 23 of theradial flow impeller 22 is exactly perpendicular relative to the planeof the picture, namely, it is also perpendicular to the axis. The blades24 can be curved or straight blades, but, in essence, they extend to theright from the base plate 23, i.e. parallel to the axis of the radialflow impeller 22.

As is usual in the case of radial flow impellers, the blades 24 are notseated on the axis, but rather, they leave the central region free sothat air can flow into this region in parallel with the axis. At thesame time, this forms the intake region of the radial flow impeller 22.Thus, the blade region is located between an inner radius, which issimultaneously the outer radius of the intake region, and an outerradius and is occupied by the blades 24. The outer radius alsocorresponds approximately to the radius of the base plate 23.

For the purposes of mechanically stabilizing the blades 24, they aresupported by a cover plate 25 at the side thereof remote from the baseplate 23. This cover plate 25 is flat in conventional radial flowimpellers. To a first approximation, the cover plate 25 of theillustrated radial flow impeller 22 is also a flat disk which isperpendicular to the axis of the radial flow impeller 22. The coverplate 25 is provided with a hole centrally thereof, this hole tooextending approximately from the inner to the outer radius of the bladeregion.

A water supply 30 is a further essential element in the combinationsteamer incorporating a steam generating system in accordance with theinvention. This water supply 30 feeds water through a water dosing means31 and a water supply line 32 into the cooking area 11. Water isexpelled at the water outlet 33, that is to say, in the vicinity of thecover plate 25 of the radial flow impeller 22. Other than in the stateof the art however, the water outlet 33 is not arranged within orbetween the base plate 23 and the cover plate 25, but rather, it isarranged outside the radial flow impeller 22 in the neighbourhood ofthat side of the cover plate 25 which is remote from the blades 24

The discharge from the water outlet 33 of the water supply 30 ispressure-free or free. As is also the case in EP 0 640 310 B1 forexample, the water now reaches an atomisation element, but this time, ina completely different position,.

If one looks simultaneously at the flow arrows 13 in the cooking area 11for the gas that has been heated by the heating element 12 and moved bythe fan 20, then one sees that it is moved from left to right at the topand bottom of the cooking area 11, i.e. away from the fan 20, whilst itis sucked in centrally and around the axis of the radial flow impeller22, i.e. it is moved from right to left in FIG. 1. This movement is alsoassisted by a metal sheet 14 which shields the heating element 12 in thecooking area 11 and thus forces the previously described direction ofthe flow arrows 13 which describe the flow path of the gas.

However, it is just this flow close to the axis in the direction of theradial flow impeller 22 of the fan 20 which also leads to the waterdroplets that have been set free at the water outlet 33 reaching theouter surface of the cover plate 25. In the embodiment illustrated here,the cover plate 25 is thus identical to the atomisation element. Thecover plate 25 rotates about the axis together with the other parts ofthe radial flow impeller 20. The peripheral speed of these components,and thus too, of the cover plate 25, leads to the water, which is nowlocated on the outer surface of the cover plate 25, flowing radiallyoutwardly and being accelerated in this diection. Consequently, thewater flows outwardly on the cover plate 25, and thus, in the case of arotating cover plate 25, upwardly and downwardly in FIG. 1 towards theviewer or away from him, that is to say, each water molecule separately,but all at the same time.

The relatively small flow rate of the water on the cover plate 25together with the simultaneously proportionately large surface area ofthe cover plate 25 leads to a very thin film of water on the coverplate. This very thin film of water eventually reaches the outermostedge of the cover plate, i.e. the outer periphery thereof. Now it isprecisely here where the highest centrifugal forces prevail.Consequently, the very thin film of water is torn off at this outermostedge of the cover plate i.e. the atomisation element 25.

It is in this way that very small water droplets develop in theatmosphere of the gas in the cooking area 11, these then rapidlyevaporate and thus produce the desired steam. Now this steam too followsthe flow arrows 13 in the cooking area 11 so that, shielded by the metalsheet 14, the steam together with the other gases is distributed firstlyin parallel with the axis to the right and then finally throughout theentire cooking area 11.

It can be seen in FIG. 1, but enlarged in FIG. 2, that the cover plate25 in a preferred embodiment of the invention is not just a flat disk.It is optional, although preferred, that the cover plate 25 should beprovided with a surface structure, in particular, with a kind ofchannel. This channel optimises the collection of the water from thewater outlet 33. As can be deduced from FIG. 2, the geometry of thearrangement is in each case radially symmetrical about the axis of theradial flow impeller 22. The channel is thus circular circumferentially.

It is not possible for the water delivered from the water outlet 33 ontothe outer surface of the cover plate i.e. the atomisation element 25 toenter the radial flow impeller 22. Hereby, consideration should alwaysbe given to the centrifugal force which is exerted on the water dropletsadhering to the cover plate 25 due to the rotation thereof. This issubstantially greater than the other forces, thus, the force of gravityfor example, which would like to move the water droplets downwardly, orthe additional force in the direction of the flow arrows 13 which isexerted by the flow of gas and which would like to draw the waterdroplets inwardly into the fan.

Due to the contour, the structure or the channel on or in the coverplate 25, the water coming from the direction of the water outlet 33 iscollected optimally and then distributed on the cover plate 25 with thehelp of the centrifugal forces. The illustrated contour is only onepossible form of design. It is preferred that attention be paid to itbeing circumferentially symmetrical in order to obtain a uniformradially symmetrical distribution of the water droplets.

Likewise, a geometry is preferred which prevents the tendency of thewater to enter the interior of the radial flow impeller 22 between thebase plate 23 and the cover plate 25 following the flow arrows 13.

A particularly preferred form is obtained if the cover plate 25 isdisposed at an angle a to the base plate 23 of the radial flow impeller22 in radially symmetrical manner. This angle a corresponds to the angle90° β, which the surface of the cover plate 25 then includes with theaxis of the radial flow impeller 22. This angle is schematicallyillustrated in FIG. 2. A contact pressure F_(a) for the water on andagainst the cover plate 25 results from the centrifugal forces F_(z),that are effective radially outwardly from the axis of the radial flowimpeller 22. Consequently, the preferred relatively small angle abetween the base plate 23 and thus the perpendicular from the axis ofthe radial flow impeller 22 on the one hand and the outwardly directedinclination of the cover plate 25 on the other now leads to the contactpressure Fa preventing premature detachment of the water droplets fromthe cover plate 25, this thus achieving maximum acceleration of thewater.

Moreover, due to the higher speed and the higher pressure, the thicknessof the water film is smaller and still smaller drops will occur when thewater film is torn off at the outer periphery. This, in turn, is ofadvantage for the formation of the steam.

The exact size of the angle a is relatively uncritical for developingthe effect, however it is preferred that the angle a should be largerthan 5° and smaller than 90°. This means that the angle β shouldpreferably be smaller than 85° and larger than 0°.

As can be perceived from FIGS. 1 and 2, the inner radius of theatomisation element 25 i.e. the cover plate is such that the latterprojects inwardly towards the blade region, i.e. it projects into theoutput region or somewhat modifies the external radius thereof, i.e. itnarrows it. Consequently, the air flow must pass through a somewhatsmaller opening than without the atomisation element 25. This leads to abetter overall flow behaviour and a more even distribution andacceleration of the water film.

Reference Symbol List

-   10 cooking device-   11 cooking area-   12 heating element-   13 flow arrows in the cooking area-   14 metal sheet-   20 fan-   21 the motor of the fan-   22 radial flow impeller-   23 base plate of the radial flow impeller-   24 blades of the radial flow impeller-   25 atomisation element in the embodiment and, simultaneously, the    cover plate of the radial flow impeller-   26 surface structure of the cover plate-   30 water supply-   31 water dosing means-   32 water supply line-   33 water outlet-   α angle of the cover plate with respect to the base plate-   β angle between the cover plate and the axis of the radial flow    impeller-   F_(Z) centrifugal force-   F_(a) contact pressure or pressure force

1. A cooking device comprising: a cooking area; one or more heatingelements; a fan which comprises a radial flow impeller having a bladeregion; a disk-shaped, axially symmetrical atomisation element whichrotates with the radial flow impeller; and a water supply whichcomprises at least one water outlet that delivers water to theatomisation element; wherein the atomisation element has an outer radiuswhich is the same as or larger than that of the inner radius of theblade region of the radial flow impeller; the atomisation element isarranged next to the blade region of the radial flow impeller in theaxial direction; and the water outlet is arranged in the neighborhood ofthe atomisation element on the side thereof remote from the blade regionof the radial flow impeller.
 2. The cooking device of claim 1,whereinthe atomisation element is provided with a radially symmetrical surfacestructure which forms a circumferential channel.
 3. The cooking deviceof claim 1, wherein the atomisation element is radially symmetrical andis arranged at an angle P to the axis of the radial flow impeller whichis smaller than 85° and larger than 0°.
 4. The cooking device of claim1, wherein the atomisation element is arranged on that side of theradial flow impeller which is remote from the neighboring wall of thecooking area.
 5. The cooking device of claim 4, wherein the atomisationelement is apertured in the center and the inner radius simultaneouslyforms the outer radius of the output region of the radial flow impeller.6. The cooking device of claim 1, wherein the atomisation elementsimultaneously forms a cover plate of the radial flow impeller.
 7. Thecooking device of claim 2, wherein the atomisation element is radiallysymmetrical and is arranged at an angle β to the axis of the radial flowimpeller which is smaller than 85° and larger than 0°.
 8. The cookingdevice of claim 2, wherein the atomisation element is arranged on thatside of the radial flow impeller which is remote from the neighboringwall of the cooking area.
 9. The cooking device of claim 3, wherein theatomisation element is arranged on that side of the radial flow impellerwhich is remote from the neighboring wall of the cooking area.
 10. Thecooking device of claim 2, wherein the atomisation elementsimultaneously forms a cover plate of the radial flow impeller.
 11. Thecooking device of claim 3, wherein the atomisation elementsimultaneously forms a cover plate of the radial flow impeller.
 12. Thecooking device of claim 4, wherein the atomisation elementsimultaneously forms a cover plate of the radial flow impeller.
 13. Thecooking device of claim 5, wherein the atomisation elementsimultaneously forms a cover plate of the radial flow impeller.